This invention relates to an apparatus and method for repowering a coal-fired steam generator, and, more particularly, to such an apparatus and method in which the combustion or boiler is repowered by incorporating a partial gasifier or carbonizer that produces a low-Btu fuel gas to power a gas turbine and a partially desulfurized char to be fired in the boiler.
Although coal fired boilers have enjoyed considerable success in supplying heat energy to steam turbines in utility plants for producing electrical energy, it has always been difficult to keep them in compliance with federal and state emissions standards. This is especially true with respect to the introduction of sulfur products into the air, especially when certain coals having high sulfur contents are used.
Since gas turbines are fairly efficient even when driven by a relatively low-Btu gas, they also lend themselves to the production of electrical energy. In these arrangements the coal is initially introduced to a partial gasifier or carbonizer which produces a relatively low-Btu gas which is passed to the gas turbine and a char which is passed elsewhere in the plant. However, one disadvantage of carbonizers is that, with some coals, only a fraction of the thermal energy in the coal can be extracted in the form of gas, while the remaining percentage leaves the carbonizer in the form of char.
The present invention is a result of the recognition that the char obtained from the carbonizer under the above-described conditions can, when properly treated, be utilized to drive the above-described boilers in a manner to considerably reduce the production of sulfur emissions. Most importantly, this invention allows repowering of an existing steam generator, increasing the total plant output of electric energy while raising the plant efficiency and reducing sulfur emissions to the atmosphere.